Computer software has impacted virtually every aspect of our lives - and so has the amount of critical software. When software annunciates safety-critical information to the human-in-the-loop or controls a system subsystem that could contribute to the loss of life, property or environment, software safety is a concern. Software system safety is a process whereby potential software or sofrware environmental causal factors contributing to system hazards are identified, analyzed, and mitigated according to their hazard priority.